1. Field of the Invention
The present invention relates to an image signal processing circuit and, more particularly, to an image signal processing circuit for an ultrasonic imaging apparatus.
2. Description of the Related Art
An ultrasonic imaging apparatus is used to scan a subject by an ultrasonic beam output from an ultrasonic transducer probe, to convert an echo signal into an image signal, and to display a tomographic image of the subject on a monitor.
A signal processing circuit for filtering an image signal is generally provided in the ultrasonic imaging apparatus in order to remove noise components. As the signal processing circuit, a frame correlation circuit for performing a frame correlation process for an image signal is used. The frame correlation circuit processes an image signal by multiplying the image signal by a fixed frame correlation coefficient.
In a conventional signal processing circuit, i.e., a frame correlation circuit for an ultrasonic imaging apparatus, however, a correlation coefficient cannot be increased in order to prevent image sharpness problems caused by a motion of a subject. For this reason, no satisfactory noise removing effect can be obtained.